THE DEVELOPMENT OF ALGORITHMS FOR ON-DEMAND MAP EDITING FOR INTERNET AND MOBILE USERS WITH GML AND SVG Miss. Ida K.L CHEUNG a, , Mr. Geoffrey Y.K. SHEA b a Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, email: [email protected] b Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, email: [email protected] Commission VI, PS WG IV/2 KEY WORDS: Spatial Information Sciences, GIS, Research, Internet, Interoperability ABSTRACT: The widespread availability of the World Wide Web has led to a rapid increase in the amount of data accessing, sharing and disseminating that gives the opportunities for delivering maps over the Internet as well as small mobile devices. In GIS industry, many vendors or companies have produced their own web map products which have their own version, data model and proprietary data formats without standardization. Such problem has long been an issue. Therefore, Geographic Markup Language (GML) was designed to provide solutions. GML is an XML grammar written in XML Schema for the modelling, transport, and storage of geographic information including both spatial and non-spatial properties of geographic features. GML is developed by Open GIS Consortium in order to promote spatial data interoperability and open standard. Since GML is still a newly developed standard, this promising research field provides a standardized method to integrate web-based mapping information in terms of data modelling, spatial data representation mechanism and graphic presentation. As GML is not for data display, SVG is an ideal vector graphic for displaying geographic data. GML sets at the back-end to store and transport data meanwhile SVG sets on front-end to render and display geographic data. The technology does not only enable the visualization of geographic data on the web, but also gives the possibility to edit geographic data online, especially via Internet and wireless environment in which GML gives a significant improvement of bandwidth, speed, access and reliability. Since both GML and SVG is text-based and vector format, it is expected that downloads can be considerably shortened and even more important for bandwidth can be substantially improved. This paper therefore seeks to investigate the capability of GML and develop a corresponding data modelling, system and prototype in order to overcome or improve the existing limitation on GIS functions. Further discussion also emphasizes on online map editing function which is still not well developed over existing web mapping system. 1. INTRODUCTION On application level, the proprietary Web mapping applications The widespread availability of World Wide Web gives the are limited to their own corporate networks and developing opportunities for delivering maps over the Internet as well as languages. The vendor-based on-line spatial services and clients small mobile devices. The sharing of spatial data through means that systems are neither interoperating with systems on Internet is important to promote interoperability of spatial data. the data level, nor the application level. Interoperability implies that there is some common concept on which information exchange and integration is based. On functional level, most Web mapping software packages can (Vckovski, 1999) perform simple GIS functions such as zooming, querying, Currently, there were over 30 different Web mapping software selecting, buffering and styling. They seldom perform more packages or solutions provided by different GIS vendors. Most advanced GIS functions such as spatial analysis and spatial popular Web Mapping packages are ESRI ArcIMS, Autodesk editing. In existing market, two Web mapping software MapGuide, GeoMedia WebMap server, and MapInfo packages, ArcIMS and Autodesk MapGuide, offer GIS MapXtreme (Peng, Z. R. and Tsou, M. H., 2003). They all have functions which are closed to editing capability on spatial data. their own proprietary data formats and different customized The ArcIMS Java Viewer using feature services has two programming languages. Some of them render images such as functions called MapNotes and EditNotes. The MapNotes GIF and JPEG but these raster data cannot be selected, changed function enables users to add text or graphics to the map. These styling or zoomed in for more detail. In term of vector data, edits are then sent to the MapNotes folder on the ArcIMS different data formats restrict the integration of data for Server. The EditNotes function enables users to edit features on applications and analyses. Moreover, different data formats the displayed map. Similar to MapNotes, once users finish support different spatial models. For instance, a particular GIS editing, the changes will be submitted to the EditNotes folder format support complex spatial model whereas another merely on the ArcIMS Server for the server administrator to review. support simple feature model. It is difficult to share data EditNotes must be converted to shapefiles or XML. MapNotes between disparate Internet systems over a wide area network. and EditNotes are therefore just graphics on map but not edited features on the server (Alex, F., 2002). For Autodesk MapGuide, functions are extended to include edit metadata, gridded data, and default styles for feature and capability by the SDF COM Toolkit to enable users to create, coverage visualization (OGC, 2003). edit, or delete actual SDF files. From the client end, the use of a MapGuide server requires downloading and installing a The overriding goad behind the implementation of GML was proprietary plug-in. Data are in proprietary format not readily providing a means for the transport and storage of geographic accessible to or useable by other applications. information, which includes both spatial and non-spatial properties of geographic features especially in Internet In short, over the Internet, it is essential to have a method of environment. Characteristics of GML are as following: storing and representing data in an open, extendable and flexible way, but also in a way that is vendor-independent. Text-based, Open and Extensible: GML documents are text b a s e d a n d e x t e n s i b l e . T h e y c a n b e e a s i l y e d i t e d , m a i n t a i n e d a n d Therefore Geography Markup Language (GML) was designed updated by any world processor. They can readily integrate to help solve above problems and promote interoperability of geospatial data with other data types such as text, voice, spatial data. GML is an XML grammar written in XML Schema graphics and video etc. Since relationships in XML elements for the modelling, transport, and storage of geographic are expressed in terms of parents and children, GML is information including both spatial and non-spatial properties of extensible to define the content inside the elements. geographic features (OGC, 2003). It is developed by Open GIS Consortium in order to promote spatial data interoperability and Encoding Feature Geometry and Properties: GML is based open standard. It is specially designed for Internet mapping on the abstract model of geography developed by OGC. The which has the potential to change how people share mapping model describes the world in terms of geographic entities called information through Internet. features. A geographic feature is “an abstraction of a real world phenomenon; it is a geographic feature if it is associated with a GML upholds the principle of separating geographic contents location relative to the Earth” (OGC, 2003). A feature consists from its presentation. This offers more flexibility in data of properties and geometries. Properties include usual name, production, handling as well as visualization. GML is used as type, value description. Geometries are composed of basic the standard of data exchange and then can be transformed into geometry building blocks such as points, lines, curves, surfaces vector format such as SVG for graphic visualization so that and polygons. In the latest version, GML 3.0 is extended to downloads can be considerably shortened and even more support 3D geometry and topological relationships also. It important for bandwidth is the scalability inherent to vector works closely to the features supported by common GIS data lines. Once on the client browser, vectors are scalable without formats. return trips to the server (Randy, 2002). The performance hence can be improved. It is essential for Web mapping which Transporting geospatial data over the Web: When the GML- requires fast delivery time and high performance. It seems that coded geospatial data are transported, all markup elements that GML and SVG are ideal for transporting and storing geographic describe all spatial and nonspatial features, geometry, and information over Internet using advanced XML technology and spatial reference systems of the data are also transported to the provide potential capability to integrate different geographic recipient. So information will not get lost and distorted in the information together. process of data transport and transformation. It is important for real time data access and transport in the Internet Environment (Peng, Z. R. and Tsou, M. H., 2003). The aim of this paper is to investigate and develop methods for generalizing map online and editing vector-formatted geospatial GML is not a data to Internet and mobile user using emerging standards – Separating content from data display: presentation language for data display. It is different from other GML and SVG. The main purposes are: GIS data formats, which separates content from data presentation. Like XML, GML can be transformed into other 1 To develop method and usage practices for generalizing vector graphics formats such as SVG for data display. The the graphic representation for geospatial data in real-time. common style engines are XSL, XSLT and CSS. This allows 2 To develop data model and algorithms for testing the different styles applied in the same GML documents.